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The original motivation for adding virNetDevIPCheckIPv6Forwarding (commit 00d28a78b5) was that networking routes would disappear when ipv6 forwarding was enabled for an interface. This is a fairly undocumented side-effect of the "accept_ra" sysctl for an interface. 1 means the interface will accept_ra's if not forwarding, 2 means always accept_RAs; but it is not explained that enabling forwarding when accept_ra==1 will also clear any kernel RA assigned routes, very likely breaking your networking. The check to warn about this currently uses netlink to go through all the routes and then look at the accept_ra status of the interfaces. However, it has been noticed that this problem does not affect systems where IPv6 RA configuration is handled in userspace, e.g. via tools such as NetworkManager. In this case, the error message from libvirt is spurious, and modifying the forwarding state will not affect the RA state or disable your networking. If you refer to the function rt6_purge_dflt_routers() in the kernel, we can see that the routes being purged are only those with the kernel's RTF_ADDRCONF flag set; that is, routes added by the kernel's RA handling. Why does it do this? I think this is a Linux implementation decision; it has always been like that and there are some comments suggesting that it is because a router should be statically configured, rather than accepting external configurations. The solution implemented here is to convert the existing check into a walk of /proc/net/ipv6_route (because RTF_ADDRCONF is apparently not exposed in netlink) and look for routes with this flag set. We then check the accept_ra status for the interface, and if enabling forwarding would break things raise an error. This should hopefully avoid "interactive" users, who are likely to be using NetworkManager and the like, having false warnings when enabling IPv6, but retain the error check for users relying on kernel-based IPv6 interface auto-configuration. Signed-off-by: Ian Wienand <iwienand@redhat.com> Reviewed-by: Laine Stump <laine@redhat.com> Reviewed-by: Cedric Bosdonnat <CBosdonnat@suse.com>
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==============================
Libvirt API for virtualization
==============================
Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
For some of these hypervisors, it provides a stateful management
daemon which runs on the virtualization host allowing access to the
API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other
languages including Python, Perl, PHP, Go, Java, OCaml, as well as
mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the
website:
https://libvirt.org
License
=======
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.
Installation
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
Contributing
============
The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
=======
The libvirt project has two primary mailing lists:
* libvirt-users@redhat.com (**for user discussions**)
* libvir-list@redhat.com (**for development only**)
Further details on contacting the project are available on the website:
https://libvirt.org/contact.html